Field
The present invention relates to a method of manufacturing a semiconductor device.
Background
To secure a certain radiofrequency characteristic of a compound semiconductor device, a so-called via hole structure which provides a conduction path from a back surface of a substrate to a source electrode on a front surface of the substrate is formed by dry etching. This via hole forming is performed ordinarily by attaching a work substrate on a support substrate with an adhesive easily soluble in a chemical solution and capable of attachment and separation even at a temperature of about 150° C. In the case of GaN-on-SiC, rather than a resist mask, a metal mask more difficult to etch than SiC is ordinarily used because of the difficult-to-etch characteristic of the SiC substrate for example, IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 32, No. 3, JUNE 2004).
In a case where a via hole is formed in a compound semiconductor device, such as CaN-on-SiC using SiC which is a difficult-to-etch material for a substrate, securing processability equivalent to that of GaAs requires a high-temperature process in which the temperature of a wafer stage on which a wafer is placed when processed is set to a temperature of 200° C. or higher by a temperature control function for the purpose of improving reactivity. However, there are presently no materials satisfying the requirements, such as a resist capable of retaining a shape even at a high temperature of 200° C. or higher and capable of being easily separated or dissolved and a wax (adhesive) not dissolved at a temperature of 150° C. or higher. For this reason, a low-temperature process of about 20° C., equivalent to that for GaAs, is necessarily used for forming a via hole in SiC.
It may be thought that the problem with a wax adhesive can be solved if direct transport is performed without using a support substrate. However, there is a need to apply a surface protective agent to protect the surface. Considering removing a surface protective agent afterward, a surface protective agent having heat resistance at about 150° C. at the highest is used. Therefore the problem with a low-temperature process cannot be avoided. This means that the processing time is increased due to a low processing rate, and that a metal mask is eventually used since any resist cannot endure processing for a long time period.
The metal mask generates a large amount of contamination, causes falls of debris from a ceiling plate onto the wafer and chamber walls, and causes a reduction in productivity, a reduction in yield and an increase in frequency of maintenance. As a solution to this problem, a method of limiting attachment of debris to a ceiling plate and chamber walls by providing a special electrode or structure (see, for example, JP 2005-535117 A and JP 8-316210A) and a method of limiting attachment by changing the plasma mode (see, for example, JP 2009-76786 A) have been disclosed.
Each of the above-described methods, however, requires extensively modifying the conventional apparatus and is incapable of radically inhibiting generation of nonvolatile products which cause falls of debris.